1. Field of Invention
This invention relates to generator/engine sets (gensets) and more particularly to methods and apparatus for reduction of nitrogen oxides and other harmful emitted gases in genset systems.
2. Description of Related Art
In conventional engines, high combustion chamber temperatures can provide conditions that facilitate the formation of nitrogen oxides (NOx). It is well known that nitrogen oxides have harmful effects on the environment.
To reduce the formation of nitrogen oxides in combustion engines such engines typically employ an exhaust gas recirculation system which feeds exhaust gas, particularly carbon dioxide, back into the combustion chamber to reduce the amount of oxygen drawn into the combustion chamber and thereby reduce one of the components required for combustion, to reduce combustion chamber temperatures. With lower combustion chamber temperatures, less nitrogen oxides are formed. However, with less oxygen being drawn into the combustion chamber, the available power from the engine is reduced.
Typically the recirculation of exhaust gas back into the combustion chamber is controlled by an EGR valve that varies the amount of exhaust gas recirculated into the combustion chamber. When particularly demanding loads are placed on the engine, EGR systems typically disable the EGR valve to prevent exhaust gas from being recirculated so that the engine can develop a suitable power output.
Certain applications of engines such as genset applications place continuous loads on an engine. If the genset is used in a hybrid vehicle, for example, additional loads for driving the vehicle are placed on the engine and these additional loads can require the engine to face greater transient loads overall, and these transient loads can require the engine to develop more power which requires more oxygen which can be obtained by simply disabling the recirculation of exhaust gas. This however, results in increased NOx emissions. The loads imposed by generators on engines in hybrid vehicles can be quite large and engines can require large variations in motive load, which can result in frequent disabling of the recirculation of exhaust gases causing a corresponding increase in production of NOx emissions.